The Atlantic Time Zone is a geographical region that keeps standard time—called Atlantic Standard Time (AST)—by subtracting four hours from Coordinated Universal Time (UTC), resulting in UTC−04:00. During part of the year, some portions of the zone observe daylight saving time, referred to as Atlantic Daylight Time (ADT), by moving their clocks forward one hour to result in UTC−03:00. The clock time in this zone is based on the mean solar time of the 60th meridian west of the Greenwich Observatory.

A Massachusetts commission concluded in 2017 that the benefits of changing to Atlantic Standard Time year-round would outweigh the disadvantages, provided that a majority of northeastern states made the same change.[4] In May 2017, the Maine Senate approved a change to AST, on the condition that there would be a referendum, and that Massachusetts and New Hampshire decided to make the same switch.[5] Also in 2017, the New Hampshire House of Representatives approved a bill in favour of a regional change, but this was voted down by the state's Senate.[6] Similar bills have been put forward in Connecticut and Rhode Island.[5]

In Florida, two bills were approved in January 2018 by House and Senate committees, to move most of the state permanently to Atlantic Standard Time (with the panhandle moving to year-round Eastern Standard Time) with no observation of daylight saving time.[7]